Singing light bulb on dimmer switch

[David D.]

Most light bulbs hum loudly when dimmed via a dimmer switch. A few are ok,
because they contain extra filament supports at critical positions.



My hanging (swag) kitchen tiffany-style light takes a G40-150w bulb. It
hums badly when dimmed.



(1) Is there a brand of G40-150 bulb that does not hum when dimmed?



(2) Alternatively, is there a small, in-line filter available, or a
filtered, table-top dimmer switch, that would create a smoother
short-duty-cycle output than the intermittent, alternating square-wave
created by a typical dimmer switch? Would that be safe for a household
lamp application? Would that eliminate the audible humming?



- David

 

[RBM]

From my experience, some lamp types whine more than others. Typically the
longer the filament stanchions are, the more vulnerable to whine the lamp
is. I've also had the best success preventing whine with Lutron dimmers

 

[David D.]

Do you really need that 150W? If you are going to dim it anyway, why
not try a 75W? It should hum less.

We normally use it at full brightness. We dim it for special moods.

A "G40" is a 5" globe with a standard hosehold lamp screw base. It
requires a higher wattage for the filament to brightly light the globe
surface (inverse square law from filament to globe surface).

 

[David D.]

From my experience, some lamp types whine more than others. Typically the
longer the filament stanchions are, the more vulnerable to whine the lamp
is. I've also had the best success preventing whine with Lutron dimmers

Thanks, RBM. I agree. I am using a Lutron table-top dimmer for my hanging
kitchen globe. The filament still sings when dimmed..

 

[Jeff Wisnia]

Most light bulbs hum loudly when dimmed via a dimmer switch. A few are ok,
because they contain extra filament supports at critical positions.



My hanging (swag) kitchen tiffany-style light takes a G40-150w bulb. It
hums badly when dimmed.



(1) Is there a brand of G40-150 bulb that does not hum when dimmed?



(2) Alternatively, is there a small, in-line filter available, or a
filtered, table-top dimmer switch, that would create a smoother
short-duty-cycle output than the intermittent, alternating square-wave
created by a typical dimmer switch? Would that be safe for a household
lamp application? Would that eliminate the audible humming?



- David

I don't think there's much you can do in a practical sense to "filter
out" the the non-sinusoidal waveform without engineering a special
purpose high chopping frequency dimmer, which would prolly waste a lot
much power in the form of heat.

BTW, it's not an alternating square wave, it's a sinusoidal waveform
which has a portion "removed" from every half cycle when you turn the
dimmer down from full brightnes. The lower you set it the less of the
original waveform is left, but the parts that are left follow the line
voltage waveform.

Before solid state stuff was a twinkle in Shockley's eye they used to
make wall mounted variac light dimmers for use in rich folks houses, and
I'd bet that they didn't make the light bulbs hum. <G>

Jeff

 

[mm]

Most light bulbs hum loudly when dimmed via a dimmer switch.

That's not been my experience.

A few are ok,
because they contain extra filament supports at critical positions.

I only have three dimmers for lights, but I've never had a lightbulb
hum because of one. Until a couple weeks ago, I was using a 150 watt
bulb in a desk lamp with a built-in dimmer right next to me.
Unfortunately, I knocked the lamp off the table and broke the bulb so
I don't have it, but I think it was the standard GE 150 watt bulb they
sell in supermarkets.

In the dining room I also have a 150 with a dimmer, and I'll check the
brand if you want me too. I only have to take off the cover. It's
probably not G-40 since I've never heard of that, so let me know if
you want me to check.

Otherwise, I'd say just try a different brand.

 

[mm]

I wonder whether a rectifier and capacitor between the dimmer and the
lamp would work (then the lamp would see DC). I bet somebody here
knows whether that would wreak havoc with the dimmer.

Since the output of the dimmer is still AC, that would dim it further.
by cutting the current in half, unless you used something like a
bridge rectifier (4 diodes arranged in a square) that is full wave.

(Sorry, maybe htat is what you mean to begin with.)

Then you'd be running yhour lightbulb on DC, and I would be very
intersted in how well that would work.

 

[Stan]

Gosh, gee.

If we are worrying about lights bulbs 'singing/humming' it makes one wonder
what other RFI (radio frequency interference) these somewhat unecessary
devices are causing? Why not use cheap bulbs and turn off a lamp or two?

And since many (most?) dimmers are manufactured 'to a price' is it correct
to assume that compromises are made?

 

[David D.]

Harold,

This is the type of technology that I was hoping was available in a fairly
small package, for home use.

I was wondering if a simple capacitor filter would smooth the rise and
fall slope.

- David

 

[David D.]

Since the output of the dimmer is still AC, that would dim it further.
by cutting the current in half, unless you used something like a
bridge rectifier (4 diodes arranged in a square) that is full wave.

(Sorry, maybe htat is what you mean to begin with.)

Then you'd be running yhour lightbulb on DC, and I would be very
intersted in how well that would work.

It would probably work, but, as a safety precaution, I would not want to try
it. With AC, one would usually survive a mometary shock. 110-volt DC can
burn severely.

- David

 

[mm]

NM,

Thanks for the offer. But I do need a G50.

A G40 is a 5" diameter globe with a standard screw base. I could use a
plain 150w bulb, but it would not be as attactive. This is an tiffany-shade
type ceiling swag over the kitchen table.

So the bulb itself shows. And it's 5 inches, so it might have a much
bigger filament than the minimum size 150 incandescent.

You might be better off removing the dimmer and buying the size you
most want to use.

I wanted the 150 for the dining area, because I only have one lamp, a
floor lamp, in my living area. It's always sort of awkward to get to
it, and sometimes near impossible, and it doesn't light up the whole
area. So I want a bright dining room bulb. If it weren't for that, I
think I'd use a 100W.

 

[D&SW]

Years ago I tried to use a bridge and two 40mF 450V caps to banish some
nasty hum coming from two chandeliers, each with five 50W bulbs. Way too
much load for the caps. The hum remained and the caps were seconds away from
exploding due to their instant heat buildup. It might have worked with a
smaller load.

 

[David D.]

Thanks, everyone, for your replies, suggestions, and electronics
clarifications.

I haven't quite decided what solution I am going to explore long term, but,
for the moment, I am using the light undimmed.

- David

 

[mm]

Years ago I tried to use a bridge and two 40mF 450V caps to banish some
nasty hum coming from two chandeliers, each with five 50W bulbs. Way too
much load for the caps. The hum remained and the caps were seconds away from
exploding due to their instant heat buildup. It might have worked with a
smaller load.

I don't get it. I thought that if the capacity of a cap was exceeded,
it just filled up on one side, and after that the rest of the current
behaved as if there were no cap. In fact it occurs to me that in a
DC power supply circuit for a radio or tv, the only reason the cap
ever gets below full charge is that the load is *high* enough to draw
more than is currently, during low parts of the cycle, being provided
through the diodes, so it drains the cap.

During the high points, the peaks of the 120 cycles per second power
(after rectification) there is more than enough power and that's when
the the caps are refilled.

Lowering the load would mean the cap would fill up on one side, and
then just stay filled all the time.

Two 40mF sounds like a lot, but if it wasn't enough, it seems to me
there would have been no current in or out of the caps after the first
charge.

If 80mF was enough to filter, maybe the internal leads couldn't handle
the current in and out without getting hot, even though current in and
out is what caps do. Maybe that level of heat was within range.

And I would also think that nothing 110 volts could do, even
full-rectified to make it higher than 110, could damage a 450V cap.

I would also wonder if caps are necessary, since an incandescent bulb
with pulsing DC current would remain hot and giving light, despite the
pulsing. Don't electronic dimmers work by completely turning off the
current parts of the time? And yet all we see is a constant but dimmer
light. They don't use caps at all except maybe little ones to make
them oscillate.


Posted and mailed because it's been almost 3 days and ahr is so busy,
I'm not sure anyone is reading this thread anymore. So I wanted the
poster to know I had replied.

 

[Bud--]

I don't get it. I thought that if the capacity of a cap was exceeded,
it just filled up on one side, and after that the rest of the current
behaved as if there were no cap. In fact it occurs to me that in a
DC power supply circuit for a radio or tv, the only reason the cap
ever gets below full charge is that the load is *high* enough to draw
more than is currently, during low parts of the cycle, being provided
through the diodes, so it drains the cap.

In this case, the cap is way too small for the 250W load, and it is well
drained before the next 'fill up'.

During the high points, the peaks of the 120 cycles per second power
(after rectification) there is more than enough power and that's when
the the caps are refilled.

Lowering the load would mean the cap would fill up on one side, and
then just stay filled all the time.

Two 40mF sounds like a lot, but if it wasn't enough, it seems to me
there would have been no current in or out of the caps after the first
charge.

Since the cap is pretty fully drained, there is a very high current at
each 'fill up' followed by high current to the load that drains the cap.

If 80mF was enough to filter, maybe the internal leads couldn't handle
the current in and out without getting hot, even though current in and
out is what caps do. Maybe that level of heat was within range.

In addition to the leads, the capacitor has an internal resistance which
you might find specified as ESR (equivalent series resistance). Trying
to filter for light bulbs causes a relatively high current charging the
caps and then discharging to the lights. That will cause heating when
flowing through the capacitor's internal resistance. A reasonably sized
(larger) filter cap would have a far smaller ESR. But the dimmer may not
like the high peak currents to charge a large cap.

And I would also think that nothing 110 volts could do, even
full-rectified to make it higher than 110, could damage a 450V cap.

The AC voltage is a sinewave whose value is constantly changing. 110
volts is the RMS value - a form of average. The peak voltage is 1.4
times that - about 155 volts, which the cap would charge to with no
load. Far lower than 450V as you said.

I would also wonder if caps are necessary, since an incandescent bulb
with pulsing DC current would remain hot and giving light, despite the
pulsing. Don't electronic dimmers work by completely turning off the
current parts of the time? And yet all we see is a constant but dimmer
light. They don't use caps at all except maybe little ones to make
them oscillate.

Dimmers work by turning on late in each 'hump' in the sine wave. The
dimmer stays on until the next zero crossing. At full brightness the
dimmer turns on at the start of the 'hump'. At low brightness the dimmer
turns on late in the 'hump' and only the end of each 'hump' is there.
Rectifying just makes all the 'humps' positive instead of half being
positive and half being negative. The same basic waveform, which causes
the singing, is still there. Capacitor filtering would change the
waveform to DC. Series inductors, which some (all?) dimmers have also
changes the waveform, and if there is enough inductance will eliminate
singing.

bud--

 

[Peter Pan]

Always thought the singing to be related to the harmonics due from
phase control (the sound isn't 60 Hz), so the capacitors might not like
seeing all that harmonic current.

Also putting a capacitor parallel to the load shouldn't make it dc. The
capacitor had to be rather large, not to mention the need for some
rectifiers. This could be a way to filter out the harmonics on the
lamp.

 

[Bud--]

Always thought the singing to be related to the harmonics due from
phase control (the sound isn't 60 Hz), so the capacitors might not like
seeing all that harmonic current.

Also putting a capacitor parallel to the load shouldn't make it dc. The
capacitor had to be rather large, not to mention the need for some
rectifiers. This could be a way to filter out the harmonics on the
lamp.

Going further back in the thread, the discussion was on filtering
rectified AC.

bud--